In bacteria belonging to the genus Streptococcus are found species that are very different in their bacteriological criteria. Thus, the methods of identification now in use make it possible using serological techniques, to classify Streptococci into different serogroups designated by the letters A to H and K to T, the groups have been found to be responsible for infections in man or animal being, in order of importance, the following: A, D, B, C, G, H, F and K.
There also exist methods of identification of these bacteria based on their nutritional characteristics. In these methods, two series of tests are applied:
Determination of the growing capacity of the bacteria in "hostile" media, the bacteria being inoculated in one or more culture media whose physical and chemical characteristics are made unusual, either by addition of inhibitors, by keeping the pH conditions very basic or by keeping the incubation temperatures abnormally low or high.
Determination of the ability to use natural carbon substrates in a complete culture medium: assimilation of simple sugars.
These identification methods have always had the drawback of requiring long implementation, which can exceed 48 hours, and their empirical nature makes them inexact.